It has been considered that the ovulation in cetaceans may be spontaneous, rather than based on a cycle. One reason is that a number of fin whales apparently have been observed to ovulate in antarctic waters during a period in which most males were not in heat. Again, increase in activity is thought to be induced by an increase in day length. Due to migration, fin whales experience increasing day lengths twice a year, once during migration to the equator in fall, and once during migration to the poles in spring. During migration to the equator, the increase in length of day would probably start the cycle. During the migration to the poles, most females are either pregnant or lactating, which inhibits ovulation.
Many cetaceans seem to ovulate and can become pregnant again immediately after giving birth, although in some lactation seems to prevent this. It appears the female has only one 'period' per year, although she may experience more if the first ovulation is not followed by pregnancy.
It is generally believed that the Cetacea retain reproductive ability until death, however some stuides have shown this may not be so. Some species have been found to show regression in parts of the ovary, mammary glands and uterus. Thus, they may experience "menopause".
The "Tuba Fallopii" (Fallopian Tubes) are more or less convoluted, and become quite wide and funnel-shaped.
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